Semiconductor and other similar industries, often use optical metrology equipment to provide non-contact evaluation of substrates during processing. One type of optical metrology is scanning white-light interferometry.
A scanning white-light interferometer uses broadband light that is split to produce a probe beam and a reference beam, which when combined produces an interference pattern. A scanning white-light interferometer images conventionally produces a plurality of images of a sample using various path differences between the combined beams. Analysis of the resulting interference fringes with respect to path difference at each pixel of the detector (which corresponds to points on the sample surface provides three dimensional information for surface height profiles of a sample. Thus, the data collected by a scanning white-light interferometry system focused to a given spot size on a given site on a semiconductor wafer contains information describing the local stack of thin films and its pattern. The spot size required for this measurement can in theory be diffraction limited.